1. Field of the Invention
This invention relates to a lens barrel of the kind having electric elements or the like mounted thereon.
2. Description of the Related Art
The conventional lens barrel of the above-stated kind has been arranged to prevent the mounted electric parts from interfering with a moving tube by arranging them either around a fixed tube which has no moving member near it or on the outside or inside of the moving tube.
The moving tube of the conventional lens barrel is mounted on the fixed tube, which serves as a holding tube, through a mechanism which includes a cam and a cam follower or a helicoid or the like, in such a manner that the moving tube moves a predetermined amount for each amount of operation performed on an operation member.
However, in the case of the conventional lens barrel mentioned above, in arranging the mounted parts within the lens barrel, a circuit board on which the parts are to be mounted must be in a flat (planar) shape where the parts are to be arranged. This requirement tends to cause an unnecessary space between the curved surface of the lens barrel and the flat surface of the mounting circuit board in arranging the mounted parts over the outer circumference of the lens barrel. The unnecessary space necessitates an increase in the outside diameter of the lens barrel by as much as that space. As a result, the size of the lens barrel increases as a whole.
The functions of cameras have recently been diversified to include an automatic focusing function, a power zooming function, etc. The number of actuators such as motors for these functions has increased. The increase in number of actuators makes control circuit arrangement complex to increase the number of parts to be mounted.
Further, the moving tube is sometimes located in the fore end of the lens barrel where a first lens group, a hood, etc., are disposed. In such a case, if an external force is accidentally applied to the lens barrel due to, for example, an incorrect operation by the operator, the external force is received by parts such as the cam and the cam follower or the helicoid that is arranged to serve as a structure for holding the moving tube in a predetermined position. Thus, the external force tends to damage the cam or the cam follower or disengage and damage the helicoid. Further, a force in the falling direction of the lens barrel tends to increase when the moving amount of the moving tube is large. A load imposed on the moving-tube holding structure then becomes larger to damage or deform it or to cause an inadequate movement of the moving tube.